The Diesel-Electric Hybrid HEMTT A3 Lean by OSHKOSH

Lean, Mean, And Green

At the Global Technology Center in Oshkosh, Wisconsin, Oshkosh engineers aggressively pursue new and better technologies for the world’s most advanced military forces. The result of this research and development is the Heavy Expanded Mobility Tactical Truck (HEMTT) A3 with its ProPulse diesel-electric hybrid system. Instead of requiring heavy batteries that like slow increases and decreases in electrical power, this diesel-electric hybrid uses ultracapacitors, which thrive on the opposite. These energy storage devices accept more of the power created by regenerative braking and deliver the power to the wheels during acceleration. According to Oshkosh, this increases fuel efficiency up to 20 percent as compared to the current HEMTT. This technology also delivers up to 120 kw of military-grade power—enough electricity to run an airfield, weapons and radar systems, a hospital, or a disaster relief command center. None of this would ever be possible, however, without the truck’s 470hp diesel engine and energy-dense fuel.

The U.S. Army has contracted Oshkosh to integrate its ProPulse hybrid-electric system with the HEMTT A3, which has the potential to make fleets less reliant on in-theater fuel convoys and trailer-mounted electrical generators.

Why Ultracapacitors Instead of Batteries?
Although Oshkosh selected ultracapacitors in this application, batteries or other storage devices could be swapped in if the situation called for it. A few advantages of ultracapacitors include:
1. They offer increased safety, since the capacitors can be brought down to 0 voltage for maintenance operations.
2. They work well in extreme temperatures ranging from -51 to 125 degrees.
3. Accelerated aging and cycling tests show they last the 25-year life of the vehicle.
4. Round trip efficiency is about 10 percent more than a comparable battery-electric hybrid, due to the ultracapacitor’s ability to recover braking energy.

The diesel engine is not mechanically connected to the wheels. Instead, it runs at an optimal rpm range and creates electrical power, which is delivered to the axle-mounted motors. When extra power is required to accelerate the vehicle, ultracapacitors kick in and deliver the burst needed. When it’s time to slow down, the motors in the axles double as generators and replenish the quick-charging capacitors. A. 340kw generator (PURPLE) B. 470hp diesel engine (GREEN) C. 1.9mj ultracapacitors for energy storage (ORANGE) D. 480 volts ac induction motors (one per axle, 4 total, BLUE)]

Photo 5/5
| The Oshkosh HEMTT A3 is fitted with the fully integrated Mobile Land-based Phalanx Weapon System (MLPWS) from Raytheon. The MLPWS recently completed a proof of concept demonstration at Yuma Proving Grounds. The Phalanx is a 14,000-pound close-range 20mm Gatling gun system originally intended for naval warships. In this truck-mounted configuration it can fire 1,500 to 2,000 rounds per minute.